This invention relates generally to calculating commands for an engine and, more specifically, to calculating a valve timing command for an engine with variable timing valve actuators.
In gasoline engines of most vehicles, each cylinder of the engine cycles through four unique stages. In the first stage, an inlet valve opens and a piston draws air and fuel through the inlet valve and into the cylinder. The inlet valve closes and the piston reverses direction in the second stage to compress the air and fuel mixture. In the third stage, a spark combusts the mixture, which drives the piston (and powers the vehicle). An exhaust valve opens and the piston once again reverses direction, in the fourth stage, to push the combusted mixture through the exhaust valve and out of the cylinder.
The controlling of the inlet valve and the exhaust valve of each cylinder is a difficult task. The engine speed, which can exceed 6,000 rpm in most vehicles, dictates that the opening and closing of the inlet valve and the exhaust valve must be able to occur up to 50 times per second. In conventional engines, cams driven by the engine actuate the inlet valve and the exhaust valve. Modern research, however, has shown that fuel efficiency and power output of the engine may be optimized with an adjustment of the valve timing for a particular load on the engine. Some variable valve timing engines have been proposed, but the theoretical fuel efficiency and output power of these engines have not yet been reached.